As a method for releasing the parts as stuck to a pressure-sensitive adhesive tape from the pressure-sensitive adhesive tape after processing, for example, there is a method for picking up a semiconductor chip as prepared by shrinking a base material and dicing it (see Patent Document 1). However, only by this method for shrinking a base material, it is difficult to reduce an adhesive strength between the diced semiconductor chip and the base material to an extent that the semiconductor chip can be easily picked up. Also, in shrinking, it is difficult to uniformly shrink the base material in the machine direction and the transverse direction. Thus, there was a problem that the semiconductor chip causes displacement and comes into contact with an adjacent semiconductor chip, resulting in breakage of the semiconductor chip.
On the other hand, heat-peelable pressure-sensitive adhesive sheets provided with a heat-expandable layer containing a foaming agent such as a heat-expandable microsphere (for example, trade names “RIVALPHA” and “RIVACLEAN”, all of which are manufactured by Nitto Denko Corporation) are used in various applications in a variety of fields. According to such a heat-peelable pressure-sensitive adhesive sheet, not only it is possible to stick and fix an adherend, thereby subjecting the adherend to desired processing, but also after processing, by expanding the foaming agent such as a heat-expandable microsphere in the heat-expandable layer by heating, thereby lowering or vanishing an adhesive strength by the heat-peelable pressure-sensitive adhesive sheet, it is possible to easily release the adherend as stuck to the heat-peelable pressure-sensitive adhesive sheet.
In such a heat-peelable pressure-sensitive adhesive sheet, in releasing the adherend from the heat-peelable pressure-sensitive adhesive sheet, a heating treatment is usually applied to the entire surface onto which the adherend sticks, thereby releasing the whole of the adherend at once. However, recently, in performing thermal release, a requirement for releasing only a part of an adherend of plural adherends as stuck to a heat-peelable pressure-sensitive adhesive sheet, while keeping the remainder in the state that it sticks to the heat-peelable pressure-sensitive adhesive sheet, is increasing.
Concretely, for example, in a processing step of the FPC (flexible printed circuit) parts having a thin-layer copper foil and a polyimide film laminated therein, a step in which after sticking and fixing the parts to a heat-peelable pressure-sensitive adhesive sheet and applying cutting processing, the subject heat-peelable pressure-sensitive adhesive sheet is thermally treated to transfer and separate a cut piece of a part of the parts is included. At this time, deformation or falling off of other cut pieces was found to occur due to vibration as generated at the time of transferring and separating the cut piece of a part of the parts. Furthermore, in a dicing step of a semiconductor wafer or a laminated capacitor, after the dicing processing, in heating the heat-peelable pressure-sensitive adhesive sheet holding the parts to release the parts, there were involved such problems that the whole of the parts including the parts which one intends to hold is separated and that displacement or falling off of the parts occurs due to vibration as generated at the time of transferring and separating the parts after processing.
Then, the present inventors proposed a thermal release method of an adherend in which in releasing an adherend from a heat-peelable pressure-sensitive adhesive sheet provided with a heat-expandable layer by heating, only a desired part of an adherend of plural adherends can be simply released, while the remainder can be kept in the state that it sticks to the heat-peelable pressure-sensitive adhesive sheet (see Patent Document 2).
[Patent Document 1]
JP-A-11-3875
[Patent Document 2]
JP-A-2002-322436